zfs-backup-server: Hard coded hostname in template

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I was just looking through your ansible roles. Learned some new tricks already, thanks for sharing.

Shouldn't this be templated?

https://github.com/whalecoiner/home/blob/7094a0f196c1206e39a4762ff06c99b85bd571d8/ansible/roles/zfs-backup-server/templates/backup.sh.j2#L9